The first goal of this project is to determine the structures of the surface proteins of the hepatitis B virus, referred to as the hepatitis B surface antigen (HBsAg), and to determine the relationship between their structures and functions both as essential viral proteins and as the important host targets for prevention of the viral disease. HBsAg is produced in large amounts during the normal course of HBV infection, a fact which has been extensively exploited: HBsAg serves as the basis for the diagnosis of HBV infection and also as the current vaccine against HBV. HBsAg consists of a "nested" set of three proteins, referred to as the S, M, and L proteins, each of which occurs in two forms due to further post-translational modifications. The structure of these will be determined following isolation of the protein from naturally infected human plasma, or following expression of the relevant protein by cloned viral DNA in eukaryotic or prokaryotic expression vectors, using a combination of physical (circular dichroism, FTIR, mass spectrometry, ultracentrifugation), chemical (Edman degradation, carboxypeptidase digestion, reduction and alkylation), and immunological (monoclonal antibody binding studies, studies of immunogenicity) techniques. The function of each of these proteins as binding proteins to cell receptors and polymerized albumin will be examined. The antigenic activity of these proteins will be examined by site specific mutagenesis, chemical modification, use of anti- synthetic peptide and monoclonal antibodies. The second goal of this project will be to utilize the information gained from the above studies to identify specific antigenic domains of the surface proteins (S,M, and L) for incorporation into novel chimeric proteins containing the cholera B toxin subunit for investigation as a potential oral immunogen against HBV. This will be done utilizing synthetic DNA fused to the Cholera B subunit gene, and expression by appropriate prokaryotic expression vectors.